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Iron and manganese oxide mineralization in the Pacific

Geological Society Special Publication 119

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Abstract

Iron, manganese, and iron-manganese deposits occur in nearly all geomorphologic and tectonic environments in the ocean basins and form by one or more of four processes: (1) hydrogenetic precipitation from cold ambient seawater, (2) precipitation from hydrothermal fluids, (3) precipitation from sediment pore waters that have been modified from bottom water compositions by diagenetic reactions in the sediment column and (4) replacement of rocks and sediment. Iron and manganese deposits occur in five forms: nodules, crusts, cements, mounds and sediment-hosted stratabound layers. Seafloor oxides show a wide range of compositions from nearly pure iron to nearly pure manganese end members. Fe/Mn ratios vary from about 24 000 (up to 58% elemental Fe) for hydrothermal seamount ironstones to about 0.001 (up to 52% Mn) for hydrothermal stratabound manganese oxides from active volcanic arcs. Hydrogenetic Fe-Mn crusts that occur on most seamounts in the ocean basins have a mean Fe/Mn ratio of 0.7 for open-ocean seamount crusts and 1.2 for continental margin seamount crusts. Fe-Mn nodules of potential economic interest from the Clarion-Clipperton Zone have a mean Fe/Mn ratio of 0.3, whereas the mean ratio for nodules from elsewhere in the Pacific is about 0.7. Crusts are enriched in Co, Ni and Pt and nodules in Cu and Ni, and both have significant concentrations of Pb, Zn, Ba, Mo, V and other elements. In contrast, hydrothermal deposits commonly contain only minor trace metal contents, although there are many exceptions, for example, with Ni contents up to 0.66%, Cr to 1.2%, and Zn to 1.4%. Chondrite-normalized REE patterns generally show a positive Ce anomaly and abundant ??REEs for hydrogenetic and mixed hydrogenetic-diagenetic deposits, whereas the Ce anomaly is negative for hydrothermal deposits and ??REE contents are low. However, the Ce anomaly in crusts may vary from strongly positive in East Pacific crusts to slightly negative in West Pacific crusts, which may reflect the redox conditions of seawater. The concentration of elements in hydrogenetic Fe-Mn crusts depends on a wide variety of water column and crust surface characteristics, whereas concentration of elements in hydrothermal oxide deposits depends of the intensity of leaching, rock types leached, and precipitation of sulphides at depth in the hydrothermal system.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Iron and manganese oxide mineralization in the Pacific
Series title:
Geological Society Special Publication
Series number:
119
Year Published:
1997
Language:
English
Contributing office(s):
Coastal and Marine Geology Program
Description:
16 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geological Society Special Publication
First page:
123
Last page:
138